In recent years, as electronic devices become highly functional, increase of a wiring housing amount is strongly demanded together with improvement of wiring density for a multilayer wiring board. In order to satisfy the demand, in the multilayer wiring board, the wiring housing amount has been increased by narrowing of a wiring width or high multilayering by increase of the number of wiring layers.
Also, as the multilayer wiring board that responds to the demand for wiring housing amount increase, there is a multi-wire wiring board for which a wiring pattern is formed of insulation coating wires (Patent Literature 1). According to the multi-wire wiring board, since the wiring pattern formed of the insulation coating wires is used, intersecting wiring within the same wiring layer is made possible, and the wiring housing amount can be increased without increasing the number of wiring layers.
In the meantime, in surface mount type components mounted on the multilayer wiring board, pitch narrowing has been advanced. In order to cope with the pitch narrowing, there is proposed a multilayer wiring board (Patent Literature 2) for which an interlayer conduction hole is formed right below a surface mount pad of the multilayer wiring board, and which is connected to an inner layer circuit through the interlayer conduction hole, or a multilayer wiring board (Patent Literature 3) for which a fan-out wiring line pulled out and wired from the surface mount pad is provided in an inner layer and connected to the interlayer conduction hole.
Also, there is proposed a multilayer wiring board including an interlayer conduction hole composed of a large hole diameter part of a relatively large hole diameter, formed from one substrate surface for mounting the surface mount type components to an inner layer, and a small hole diameter part of a relatively small hole diameter, formed from the inner layer to the other substrate surface (Patent Literature 4).